<!doctype html>
<html>
<head>
	<meta charset="UTF-8" />
	<title>Document</title>
	<style type="text/css">
		*{
			padding: 0;
			margin: 0;
		}
		body{
			background: greenyellow;
		}
		.container{
			width: 1200px;
			margin: auto;
			overflow: hidden;
		}
		.col{
			width:32.333333% ;
			height: 50px;
			background: cornflowerblue;
			float: left;
			text-align: center;
			line-height: 50px;
			border: 1px solid red;
		}
		/*.container::after{
			content:"";
			display: table;
			clear: both;
		}*/
		@media (max-width:500px){
			.col{
				width: 100%;
				margin-top: 10px;
			}
				body{
					background: khaki;
			}
			.container{
				width: 100%;
			}
		}
	</style>
</head>
<body>
	<div class="container">
		<div class="col"><a href="lifangti.html">左边</a></div>
		<div class="col">中间</div>
		<div class="col">右边</div>
	</div>
</body>
</html>